/Engine/Plugins/2D/Paper2D/Source/Paper2D/Classes/PaperFlipbook.h
Returns the keyframe index that covers the specified time (in seconds), or INDEX_NONE if none exists. When bClampToEnds is true, it will choose the first or last keyframe if the time is out of range.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintCallable, Category="Sprite") int32 GetKeyFrameIndexAtTime ( float Time, bool bClampToEnds ) const